I have a question about String.prototype.toLocaleLowerCase() ;

I want to use toLocaleLowerCase() with locale parameter like here

But I get this error.

lib.es5.d.ts

Could you help me, please?

Package and System Info:

cli packages: (C:\Users\Ahmet\AppData\Roaming\npm\node_modules)

@ionic/cli-utils  : 1.18.0
ionic (Ionic CLI) : 3.18.0

global packages:

cordova (Cordova CLI) : 7.1.0

local packages:

@ionic/app-scripts : 3.0.0-201710070411
Cordova Platforms  : android 6.2.3
Ionic Framework    : ionic-angular 3.7.1

System:

Node : v8.7.0
npm  : 5.5.1
OS   : Windows 10